revlogdeltas: split candidate groups selection from the filtering logic
The group iteration has two main components:
* walking candidates, the logic that we are about to extend to build
intermediate snapshots,
* Making sure we test diffs against interesting bases. No duplicated tests,
skipping empty revisions, etc.
We split `_candidategroups` to separate the two components. This achieves two
goals:
* It will be simpler to update the walking logic for intermediate snapshots,
* We can gather the filtering logic from `finddeltainfo` into
`_candidategroups` to centralize it.
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}